Design and Implementation of a Compact Digital Frequency Modulator in an ASIC

In this paper, we present a digital frequency modulator designed and fabricated within the Tiny Tapeout application-specific integrated circuit (ASIC) framework, which serves as a hands-on example of ASIC development for radio electronics education. To overcome the constraints of the framework, namely limited silicon area and clock frequency, we propose a direct digital synthesis (DDS) frequency modulator featuring a highly area-optimized phase-to-sine amplitude algorithm. Additionally, we present a complete hardware prototype of the modulator, developed for both demonstration and educational purposes. For ease of use, the prototype includes a USB interface that functions as a standard USB sound card, enabling the transmission of a radio frequency-modulated audio signal that resembles FM radio broadcasting.